Expand and simplify: (x−1)(x+1)+x(x - 1)(x + 1) + x(x−1)(x+1)+x.
x2+x−1x^2 + x - 1x2+x−1
x2−1x^2 - 1x2−1
x2+x+1x^2 + x + 1x2+x+1
2x2+x−12x^2 + x - 12x2+x−1